Microstructural and Mechanical Evaluation of Near γ-TiAl Alloys Containing Molybdenum and Rhenium

Abstract

Near y-TiAI alloys which incorporated Cr, and Mo or Re additions [Ti-48Al-2Cr-1.5Mo-0.1Y, Ti-48A1-2Cr-1.5Re-0.1Y, and Ti-46A1-2Cr-1.5Re-0.1Y(at.%)1, were prepared by arc casting and hot isostatic pressing; then heat treated at 1200 and 900°C to produce a duplex microstructure. All three alloys contained a bimodal size distribution of B2 phase, which was enriched in Cr+Mo or Cr+Re. Very little a2 was present in the 48A1 alloys; whereas the 46Al, 1.5Re alloy contained areas of transformed lamellar a 7 jy, within which short lengths of B2 periodically interrupted the a2 plates. The composition of both the equiaxed and lamellary in each alloy was 49±0.5Al, 1.6±0.4Cr and asl.2Mo or <lRe(at%). Similarly, the composition of the B2 in the three alloys was experimentally equivalent: 33±1A1, 8.5±2Cr and 6.5±1.5Mo or Re(at%). In the Re containing alloys, the a2 composition was 33Al, 1.7±0.3Cr, and 0.5±03Re. Room temperature tensile ductilities were low, ranging from 0.5 to 1%; while ultimate strengths approached 500MPa [7x10 4 s 1 strain rate]. Testing at 700°C produced little change in alloy strength, while ductility increased to as much as 2.5%.